Doing so is impossible “out-of-the-box” because dom0 doesn’t have network interfaces (it would also defeat the purpose of Qubes OS as a whole).
That said, if your goal is - say - screencasting Qubes OS to a classroom and you don’t care about the data that is on your machine, you might be able to install Qubes OS as a virtual machine (like what’s done with Qubes OS’ openQA in KVM) and record/screencast the screen from there.
Else, the easiest way would probably be to buy a hardware HDMI/Displayport to WiFi dongle.
The links below might be of interest - although they’re about accessing dom0 remotely, not screencasting its content - but you might then be able to screencast the remote desktop with another machine or a dedicated qube: